Being superior to glass in lightness and processability, such transparent resins as (meth)acrylic resin (e.g., polymethyl methacrylate), clear epoxy resin, and clear silicone resin have been widely used for aircraft windshields, clear containers, and clear coating materials.
Recently, they also have found use as transparent resin lenses for spectacle glasses in the optical field.
Also, in the field of optoelectronic materials, the aforesaid transparent resins are being commonly used for antireflective coating of liquid crystal displays, transparent coating of solar cells, light-emitting diodes, and CCD and CMOS sensors. Such optoelectronic materials usually need not only transparency but also high refractive indices for efficient light emission and light collection.
Unfortunately, conventional transparent resins are given somewhat controlled mechanical properties by crosslinking or the like but they need special techniques if they are to have improved optical properties, especially refractive index.
Such special techniques include addition of a large amount of such heavy atoms as bromine and sulfur to an organic resin for its improvement in refractive index, as disclosed in Patent Documents 1 and 2.
Another way for improvement of refractive index is by dispersion of high refractive inorganic oxide fine particles into an organic resin, as disclosed in Patent Documents 3 and 4.
The technique disclosed in the foregoing Patent Documents 1 and 2 suffers the disadvantage that the resulting organic resin is unstable to heat and light and vulnerable to degradation, such as discoloration, after use for a long period of time. In addition, the resulting organic resin is liable to corrode electrodes when it is used for electronic parts.
Also, the technique disclosed in Patent Documents 3 and 4 involves problems with long-term storage stability in the resulting resin containing fine particles dispersed therein. Moreover, it needs a large amount of dispersing stabilizer that ensures the stable dispersion of inorganic oxide fine particles in the resin. This poses a problem with balancing the refractive index against the dispersion stability.
Incidentally, there is known a resin composition (not intended for high refractive index) produced from a polymerizable triazine compound, as disclosed in Patent Documents 5 and 6.